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SOLAR MICROWAVE DRIFTING SPIKES AND SOLITARY KINETIC ALFVEN WAVES

SOLAR MICROWAVE DRIFTING SPIKES AND SOLITARY KINETIC ALFVEN WAVES. D. J. Wu, J. Huang, J. F. Tang, and Y. H. Yan The Astrophysical Journal, 665: L171–L174, 2007 August 20 presented by Gelu M. Nita. Motivations for selecting this paper.

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SOLAR MICROWAVE DRIFTING SPIKES AND SOLITARY KINETIC ALFVEN WAVES

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  1. SOLAR MICROWAVE DRIFTING SPIKES AND SOLITARY KINETIC ALFVEN WAVES D. J. Wu, J. Huang, J. F. Tang, and Y. H. Yan The Astrophysical Journal, 665: L171–L174, 2007 August 20 presented by Gelu M. Nita

  2. Motivations for selecting this paper • Mechanisms driving eruptive phenomena and elementary processes occurring at the smallest coherent scales have been outstanding problems in solar physics. • In this Letter, a novel kind of fine structures of solar radio bursts, “solar microwave drifting spikes” (SMDSs), is reported. • The frequency range in which these structures were observed and the frequency and time resolutions of the observing instrument exactly match the observational abilities of the NJIT’s FST instrument. • If proven correct, the interpretation presented in this Letter may provide diagnostics for some characteristic parameters of solar corona in the flaring region, which may be applied if similar events are observed by FST.

  3. DATA Solar Broadband Radio Spectrometer (SBRS) National Astronomical Observatories of China (NAOC) 1.25 ms temporal resolution 4 MHz frequency resolution 1.10–1.34 GHz freq. range 2004 November 3 03:25:7.5 to 03:25:10.2 UT NOAA AR 10696 N09E45 65 individual SMDSs from 1.112 to 1.268 GHz

  4. Data Analysis • RCP & LCP central frequencies • Lifetime • Relative bandwidth • Drift rate

  5. Interpretation The analysis shows that the SMDSs can be produced by a group of “solitary kinetic Alfve´n waves” (SKAWs) with small cross-field scales, in which the electrons in the SKAWs are accelerated self-consistently by the SKAW electric fields to tens of keV and trapped within the SKAW potential wells. It is these trapped electrons that trigger the SMDSs via the Electron Cyclotron Maser Emission (ECME) mechanism, and the frequency drifts of the SMDSs are attributed to the SKAW propagation along the magnetic field. The SKAWs are exact solutions of two-fluid equations for a low- plasma and have been experimentally verified in the magnetosphere, where they accelerate auroral electrons to several keV. The authors believe the SMDSs represent a new observational signature of SKAWs in the solar atmosphere.

  6. Moving SKAW trap Loss cone distribution of the trapped electron momentum Interpretation Radiation generated by the Electron Cyclotron MASER emission mechanism

  7. Theoretical structure of a SKAW • Relative density • Parallel electric field • Electric potential • Electron velocity inside a SKAW

  8. Derived parameters • df/f => local Alfven velocity vA=6×103 km/s longitudinal source size 4Km transversal source size 10m • vA => energy of trapped electrons 50 keV SKAW frequency 1.5×103 Hz • <f> => mean source magnetic field Bs~100G • vA ,<f> => plasma density n0 =1.3×109 cm-3 • n0 => trapped electron density n0 =1.3×108 cm-3

  9. Microwave spikes observed by FSTDecember 06, 2006, 19:41 UT DATA Zoom in somewhere in the 1-1.5 GHz range 1MHz frequency resolution 100s integration time 20ms time resolution PRELIMINARY RESULTS <df/f>(0.35±0.28)% 20,000 spikes/minute! Spike lifetime <20ms Almost 100% circular polarization No obvious drift

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